fix quoting in set-image commit

Using double quotes means backquotes are interpolated as a shell
command.

Author: haarg

.github/workflows/set-image.yml

@@ -52,6 +52,6 @@ jobs:
         run: |
           kustomize edit set image ${{ inputs.base-tag }} ${{ inputs.tag }}
           git add .
-          git commit -m "Update ${{ inputs.app }} to `${{ inputs.tag }}`"
+          git commit -m 'Update ${{ inputs.app }} to `${{ inputs.tag }}`'
       - name: Push manifests
         run: git push